Hirschberg test
The Hirschberg test estimates the angle of a strabismus from the position of the corneal light reflex, the first Purkinje image.1 The patient fixates a spotlight at 33 cm, and the examiner compares the reflex in the deviating eye with the reflex in the fixating eye.2
The reflex lies on the nasal side of the deviated eye in exotropia and on the temporal side in esotropia.1 The reflex lies below the corneal center in hypertropia and above the center in hypotropia.1 Hirschberg calculated 7° of deviation for each 1 mm of decentration.1 Other estimates range from 7° to 15° per millimeter.3 Clinical guides convert each millimeter to 12 to 15 prism diopters, or to about 20Δ (11°).2,3
The test suits patients too young for the prism and cover test and patients whose poor acuity prevents adequate fixation.1 The result is approximate because accommodation cannot be controlled, the angle kappa is included in the measurement, and observers read the reflex position differently.1
More detail
The usual diagram of the method assumes an angle lambda of zero, although angle lambda is typically 13.75Δ at birth and falls to 9Δ by 5 years old.3 The examiner therefore notes the reflex in the non-amblyopic eye, with the other eye covered, before judging the reflex in the strabismic eye.3 The Krimsky method modifies the test by placing prisms before the deviating eye until the reflexes occupy the same relative positions.3 Both methods are imprecise, and deviations of up to 14Δ may be overlooked.3
Sources (6)
- von Noorden and Campos, Binocular Vision and Ocular Motility, ch. 12
- Practical Binocular Vision Assessment, ch. 6
- Pickwell's Binocular Vision Anomalies, ch. 3
- Caloroso, E.E., Rouse, M.W. (1993). Clinical Management of Strabismus. Butterworth-Heinemann.
- Rutstein, R., Daum, K. (1997). Anomalies of Binocular Vision: Diagnosis & Management, Mosby.
- Scheiman, M., Wick, B. (2014). Clinical Management of Binocular Vision: Heterophoric, Accommodative, and Eye Movement Disorders. 4th ed., Lippincott Williams & Wilkins.
Reviewed October 2026